Pearlescent pigments are a pigment with pearly luster made by coating a sheet substrate with one or more metallic oxides, and different oxides and oxide thicknesses can lead to different pearl effects. At present, the vast majority of iron pearlescent pigments take ferric trichloride as a coating iron oxide precursor, and the vast majority of titanium pearlescent pigments take titanium tetrachloride as a coating titanium dioxide precursor.
Ilmenite is an oxide ore of titanium and iron, and is the main ore for smelting titanium. At present, the titanium tetrachloride or titanyl sulfate is mainly prepared by using chlorination method or sulfuric acid method, and further refined for removal of impurities. The chlorination method comprises: mixing a high-titanium slag with petroleum coke at a certain ratio, crushing. and reacting the mixture by introducing a chlorine gas to generate a titanium tetrachloride gas, condensing the titanium tetrachloride gas to obtain a liquefied titanium tetrachloride liquid, filtering and distillating the titanium tetrachloride liquid to obtain a titanium tetrachloride finished product. The sulfuric acid method comprises infiltrating ore with a sulfuric acid to generate a large amount of waste acid and ferrous sulfate.
At present, there are two methods for the research of dissolving ilmenite with a hydrochloric acid. One is, as a previous step of the sulfuric acid method, at the condition of a high temperature and low acid ore ratio, dissolving the impurities in the ilmenite, then precipitating titanium in the form of a metatitanic acid after dissolution to serve as a raw material in the next step of dissolving by sulfuric acid, see e.g. Patents CN 1766137A, CN 101935063A, CN 102602991A, CN 102616842A, etc. The other one is directly dissolving the ore with a hydrochloric acid, and then separating titanium oxydichloride by extraction, see e.g. U.S. Pat. Nos. 3,236,596, 4,269,809, 6,500,396B1, 6,375,923, CN101935063A, etc. These methods are all used directly in the production of synthetic rutile, rather than pearlescent pigment coating.